Known optical analysis techniques such as reflectometry and ellipsometry involve reflection measurements. Also many apparatuses are commercially available for enabling these techniques.
But these apparatuses are designed for performing the reflection measurements on samples with planar reflecting faces. For example, the measured samples are silicon wafers provided with thin films as used for microelectronic applications. They may also be flat glass samples with coatings, for example in view of manufacturing architectural or automotive glazings, or also display panels.
However, reflection measurements performed on eyeglasses are required, in particular for quantifying a residual reflection of eyeglasses which are provided with antireflecting coatings, and for quantifying a protection efficiency which is provided to an eyeglass wearer against UV-radiation hazards. For eyeglasses with antireflecting coatings, the measurements deal with visible radiations, namely in the wavelength range comprised between 380 nm (nanometer) and 780 nm, and incidence angle values equal to or less than 17° (degree). For UV-protection rating, the measurements deal with UV-A and UV-B radiations, with wavelength values of between 280 nm and 380 nm, and incidence angle values such as 30° and even 45°.
But due to the curved shapes of eyeglass faces, either concave or convex, the currently available apparatuses do not allow performing reflection measurements on eyeglasses. Indeed, these apparatuses are not designed for exposing to a measurement light beam a face of a sample which is curved, and controlling a height of the sample face at the location of the measurement in this face. In addition, the curvature of the sample face causes errors in the measurement result if no attention is especially drawn on the optical consequences of the curvature of the measured face.
Starting from this existing situation, one object of the present invention is to allow reflection measurements for eyeglasses in a simple and efficient manner, and with high measurement accuracy.
Another object of the invention is to allow using one and same apparatus for quantifying the residual reflection of an eyeglass provided with an antireflecting coating effective in the visible wavelength range, but also for rating the UV-protection which is provided to an eyeglass wearer.
Still another object of the invention is to measure reflection on an eyeglass without damaging the eyeglass or requiring permanent alteration of the eyeglass.